Adjust the safety comments on drain/into_iter_from

The safety contract for these methods is really about the validity of
the given `RawIter` for this `RawTable`. Once that's established, the
lifetime is no longer a concern, since `RawDrain<'_, T>` has a borrow
and `RawIntoIter<T>` is a consuming owner.

Author: cuviper

src/raw/mod.rs

@@ -1073,12 +1073,10 @@ impl<T> RawTable<T> {
     /// Returns an iterator which removes all elements from the table without
     /// freeing the memory.
     ///
-    /// It is up to the caller to ensure that the `RawTable` outlives the `RawDrain`.
-    /// Because we cannot make the `next` method unsafe on the `RawDrain`,
-    /// we have to make the `drain` method unsafe.
-    ///
     /// Iteration starts at the provided iterator's current location.
-    /// You must ensure that the iterator covers all items that remain in the table.
+    ///
+    /// It is up to the caller to ensure that the iterator is valid for this
+    /// `RawTable` and covers all items that remain in the table.
     #[cfg_attr(feature = "inline-more", inline)]
     pub unsafe fn drain_iter_from(&mut self, iter: RawIter<T>) -> RawDrain<'_, T> {
         debug_assert_eq!(iter.len(), self.len());
@@ -1092,12 +1090,10 @@ impl<T> RawTable<T> {
 
     /// Returns an iterator which consumes all elements from the table.
     ///
-    /// It is up to the caller to ensure that the `RawTable` outlives the `RawIntoIter`.
-    /// Because we cannot make the `next` method unsafe on the `RawIntoIter`,
-    /// we have to make the `into_iter_from` method unsafe.
-    ///
     /// Iteration starts at the provided iterator's current location.
-    /// You must ensure that the iterator covers all items that remain in the table.
+    ///
+    /// It is up to the caller to ensure that the iterator is valid for this
+    /// `RawTable` and covers all items that remain in the table.
     pub unsafe fn into_iter_from(self, iter: RawIter<T>) -> RawIntoIter<T> {
         debug_assert_eq!(iter.len(), self.len());